Bypass valve for hydraulic jacks



March 28, 1967 c. CRISP BYPASS VALVE FOR HYDRAULIC JACKS 2 Sheets-Sheet1 Filed Dec. 27, 1965 INVENTOR. CHESTER A. CRISP T a 7. PW 2 ATTORNEYSMarch 28, 1967 c. A. CRISP BYPASS VALVE FOR HYDRAULIC JACKS 2Sheets-Sheet 2 Filed Dec. 27, 1965 INVENTOR. CHESTER A. CRISP I "9%,? WHORNEYS United States Patent Ofiice 3,311,026 Patented Mar. 28, 19673,311,026 BYPASS VALVE FOR HYDRAULIC JACKS Chester A. Crisp, Wilmington,Ill., assignor to Caterpillar Tractor Co., Peoria, 111., a corporationof California Filed Dec. 27, 1965, Ser. No. 516,619 2 Claims. (Cl.91-401) This invention relates to hydraulic jacks and particularly toimprovements in the bypass valves employed in some jacks to relieve theshock when the piston reaches the end of its travel and abuts the end ofthe cylinder.

It is common practice to provide double acting check valves controllingflow through passages which extend through the piston of a hydraulicjack. Such valves have stems projecting from opposite sides of thepiston. They are held closed by actuating pressure on one side of thepiston and, when the piston approaches the end of its stroke, they areopened by engagement of the stems with the end of the cylinder or a partthereof. This permits bleeding of actuating pressure to the low pressureend of the jack and to a sump so that only enough pressure remains tohold the piston in its load sustaining position.

The valves described above often relieve or bypass too much fluid tooquickly so that the piston travels on by pressure and inertia to the endof its stroke where shock is produced which is damaging to the jack andits supporting structure.

It is the object of the present invention to improve bypass valves ofthe kind described by simple and inexpensive means in a manner tomodulate the fiow of bypassed fluid and thus decrease the speed of thepiston prior to bypassing the full capacity of the valves.

The above and further objects and advantages of the invention are madeapparent in the following specification wherein the invention isdescribed in detail by reference to the accompanying drawings.

In the drawings:

FIG. 1 is a view in side elevation of the front portion of a track-typetractor with a bulldozer secured thereto and illustrating a conventionaljack for raising and lowering the bulldozer blade with respect to theground;

FIG. 2 is an enlarged fragmentary sectional view of the jack shown inFIG. 1 illustrating valves embodying the present invention controllingflow of fluid through the jack piston;

FIG. 3 is a fragmentary detail showing a constructional feature of oneof the valves shown in FIG. 2; and

FIG. 4 is a sectional view taken on the line IV-IV of FIG. 3.

In FIG. 1, the forward end of a tractor indicated generally at is shownas supporting a bulldozer blade 11 by means of push arms 12 which may beraised and lowered about their pivotal connections 13 with truck frames14 of the tractor, there being only one push arm and connection shown inFIG. 1. A tilt brace is only partially shown at 15 and a hydraulic jack16 is provided for raising and lowering the blade. The jack is pivotallysupported on a trunnion 17 shown in dotted lines and supported on abracket 18 which is secured to the radiator guard 19 of the tractor.

The jack has the usual piston and extensible rod 20 pivoted to the blade11 as at 21. The jack is of the double acting type and fluid from asuitable source under pressure, which is not shown, may be introduced toeither end of the jack for raising and lowering the blade. When a jackof this type is fully extended or fully retracted under the highpressures required for operating devices of this type, an undesirableshock is often encountered as the piston reach-es the end of the strokeand damage results not only to the jack but to associated parts of thetractor itself. It has been common practice to provide ports extendingthrough the piston from the rod end to the head end of the cylinder andto control flow through these ports with double acting check valves ofthe kind shown in FIGS. 2, 3 and 4.

In FIG. 2, the jack piston is shown at 23 as fitted over a reduced endof the rod 20 and secured thereon as by a nut 24. The piston isgenerally of solid material With suitable seals such as shown at 25 and26 and has ports extending therethrough for reception of check valves 27and 28 which have stems 29 and 30, respectively, guided in sleeves 31pressed into opposite ends of the port. The sleeves are retained inposition by washers 33 and 34 encircling the reduced portion of theshaft 20 and overlying the edges of the sleeves. The sleeves aregenerally hollow and have cutaway portions, best shown in FIGS. 3 and 4at 35, communicating with their interiors to permit flow of fluid fromone side of the piston to the other. Thus as the piston approaches theend of its stroke in either direction, the projecting ends of the valvestems 29 and 30 engage the end of the cylinder being approached and thevalves, having been held closed by the pressure which causes the stroke,are opened to bleed pressure to the opposite sides of the piston. Forexample with pressure on the rod side of the piston as indicated in FIG.2, the valves are normally urged to the closed position such asillustrated for the valve 28 and as the end of the stroke is approached,the valves are opened to the position shown in connection with the valve27 to permit bleeding of pressure from the rod side to the head side andthis pressure is exhausted as through a passage 36 and conduit 37through which it is returned to the sump (not shown). One disadvantageof the earlier bypass valves of this type was that both valves engagedthe end of the cylinder at the same time and were opened simultaneouslyso that a great deal of pressure was exhausted at once and the force offluid behind the piston as well as inertia cause it to strike the end ofthe cylinder with -a resultant destructive shock.

The improvement of the present invention resides in providing one of thevalves, this being the valve 27 in FIG. 2, with a stem which isconsiderably longer in both directions than the stem of the other valve.Consequently as the piston approaches the end of the stroke, this stemis engaged first and the one valve opened first bleeding a smallquantity of fluid thus reducing speed prior to opening of the secondvalve. Consequently the inertial force has been reduced and contactbetween piston and the end of the cylinder is prevented.

The present disclosure shows the piston as having two ports and twovalves but obviously any number of valved ports may be employed and anydesired number of the valves mayhave longer stems for producing themodulating effect which is produced by opening of one or more valvesprior to opening of the others.

What is claimed is:

1. In a hydraulic jack having a piston rod and piston and check valvesin the piston which are closed by pres- 3,311,026 3 4 sure on eitherside of the piston and having stems pro- References Cited by theExaminer jecting from the piston for engagement with the end UNITEDSTATES PATENTS of the, cylinder at the opposite side of the piston tore-' duce, shock when the piston approaches the end of its 841'5271/1907 Imler 91-422 7 stroke, the improvement which comprises means for5 1,985,361 12/1934 Anthony et a1 91-401 opening one of said checkvalves prior to opening others 2752'890 7/1956 Rogneby 91 401 tomodulate the escape of pressure through the'piston 290L007 9/1959ROFkWeH 91 401 and reduce the shock occurring at the end of its stroke.3,182,563 5/1965 Nellan 91401 2. The combination of claim 1 in which themeans for opening is a stem on said one check valve which is longer 10MARTIN SCHWADRON Primary Exammer' than that of the others. P. E.MASLOUSKY, Assistant Examiner.

1. IN A HYDRAULIC JACK HAVING A PISTON ROD AND PISTON AND CHECK VALVESIN THE PISTON WHICH ARE CLOSED BY PRESSURE ON EITHER SIDE OF THE PISTONAND HAVING STEMS PROJECTING FROM THE PISTON FOR ENGAGEMENT WITH THE ENDOF THE CYLINDER AT THE OPPOSITE SIDE OF THE PISTON TO REDUCE SHOCK WHENTHE PISTON APPROACHES THE END OF ITS STROKE, THE IMPROVEMENT WHICHCOMPRISES MEANS FOR OPENING ONE OF SAID CHECK VALVES PRIOR TO OPENINGOTHERS TO MODULATE THE ESCAPE OF PRESSURE THROUGH THE PISTON AND REDUCETHE SHOCK OCCURRING AT THE END OF ITS STROKE.